THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP96/03629.
The present invention relates to an ultrasonic flowmeter for measuring the flow rate of a fluid and an ultrasonic transducer used therein, by disposing a pair of ultrasonic transducer sets at the upstream side and downstream side of the fluid each, transmitting an ultrasonic wave from one ultrasonic transducer, and receiving by other ultrasonic transducer.
Traditionally the technology for measuring the flow rate of a fluid flowing in a piping by using ultrasonic wave has been developed. An ultrasonic flowmeter is known in a constitution as disclosed as xe2x80x9cTrial fabrication of ultrasonic flow meter for gasxe2x80x9d in Measurement Research Report Vol. 26, No. 1, pp. 1-6, Japan.
Conventional ultrasonic flowmeter and ultrasonic transducer are described below.
FIG. 20 shows a constitution of a conventional ultrasonic flowmeter, and FIG. 21 shows a constitution of a conventional ultrasonic transducer for gas. In FIG. 20, reference numeral 51 is a cylindrical tube, 52 is an ultrasonic transducer A, 53 is a mounting port A for mounting the ultrasonic transducer A 52 on the cylindrical tube 51, 54 is an ultrasonic transducer B, 55 is a mounting port B for mounting the ultrasonic transducer B 54 on the cylindrical tube 51, and 56 is a fluid to be measured flowing in the cylindrical tube 51. In FIG. 21, reference numeral 57 is a cylindrical piezoelectric plate, 58 is a matching layer, and 59 is a lead wire.
In thus composed ultrasonic flowmeter, the constitution is described below.
Through the mounting port A 53 and mounting port B 55, the ultrasonic transducer A 52 and ultrasonic transducer B 54 are mounted on the cylindrical tube 51 obliquely opposite to each other. Supposing the distance between the ultrasonic transducer A 52 and ultrasonic transducer B 54 to be L, the angle formed between the longitudinal direction of the cylindrical tube 51 and propagation direction of ultrasonic wave to be xcex8, the sound velocity of ultrasonic wave propagating through the fluid 56 in windless state to be C, and the flow velocity of the fluid 56 to be V, the propagation time t1 of the ultrasonic wave transmitted from the ultrasonic transducer A 52 propagating through the fluid 56 until received by the ultrasonic transducer B 54 is expressed as follows.                               C          +                      V            ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢            θ                          =                  L          t1                                    (                  Formula          ⁢                      xe2x80x83                    ⁢          1                )            
Similarly, the propagation time t2 of the ultrasonic wave transmitted from the ultrasonic transducer B 54 propagating through the fluid 56 until received by the ultrasonic transducer A 52 is expressed as follows.                               c          -                      V            ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢            θ                          =                  L          t2                                    (                  Formula          ⁢                      xe2x80x83                    ⁢          2                )            
Canceling the sound velocity C of the fluid 56 from the two formulas, the following expression is obtained.                                           1            t1                    -                      1            t2                          =                              2            ⁢            V            ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢            θ                    L                                    (                  Formula          ⁢                      xe2x80x83                    ⁢          3                )            
From the above formula, the flow velocity V of the fluid 56 is obtained as follows:                     V        =                              L                          2              ⁢              cos              ⁢                              xe2x80x83                            ⁢              θ                                ⁢                      (                                          1                t1                            -                              1                t2                                      )                                              (                  Formula          ⁢                      xe2x80x83                    ⁢          4                )            
Since this expression does not include the sound velocity C of the fluid 56, the flow velocity V is obtained regardless of the material of the fluid 56, and the flow rate is deduced from the obtained flow velocity V and the sectional area of the cylindrical tube 51. The ultrasonic transducer used when the fluid 56 is gas is cylindrical in shape as shown in FIG. 21, and comprises a cylindrical piezoelectric plate 57 and a single matching layer 58.
Such conventional constitution, however, involves the following problems.
(1) In a first problem, since the piezoelectric plate used in the ultrasonic transducer is cylindrical, when the thickness vibration or radial vibration of a disk is utilized, if a low frequency is selected, the diameter becomes large, and the ultrasonic transducer is large in size, so that the ultrasonic flowmeter cannot be reduced in size. When using the ultrasonic transducer of small size, the frequency must be high, and effects of attenuation due to propagation of ultrasonic wave are significant, which causes to increase the cost of circuit of the ultrasonic flowmeter. Accordingly, when an ultrasonic transducer of a proper size suited to the ultrasonic flowmeter is selected, the selection of the frequency is limited. Moreover, the electromechanical coupling coefficient of thickness vibration of disk is Kt, and the electromechanical coupling coefficient of radial vibration is Kp, which were smaller than the electromechanical coupling coefficient of longitudinal vibration of K33, and hence the sensitivity was low. Yet, since the cylindrical piezoelectric plate 57 was not provided with constituent material such as backing layer for lowering the mechanical Q, only ultrasonic pulses of long ringing could be transmitted, and it was hard to shorten the flow rate measuring time.
(2) In a second problem, since the section of the cylindrical tube 51 is circular, in spite of the two-dimensional flow velocity distribution in which the flow velocity V near the center is fast and the flow velocity V of the outer side is slow, at the flow velocity V obtained by two confronting sets of ultrasonic transducer, it is hard to reflect the flow velocity distribution of the entire section of the cylindrical tube 51, and the average flow velocity is only in the measuring region in the section of the cylindrical tube 51. Since the flow rate in the cylindrical tube 51 is determined from the measured flow velocity V by using an approximate formula, it is hard to estimate the flow velocity distribution at high precision, and it is hard to obtain a high precision of measurement of flow rate.
The invention is to solve the problems of the prior art, and it is an object thereof to present a compact ultrasonic flowmeter and ultrasonic transducer, advanced in degrees of freedom of selection of dimensions and frequency of ultrasonic transducer, high in sensitivity, and excellent in high speed response and precision.
The invention includes a flow passage, and an ultrasonic transducer disposed for measuring the flow rate of the fluid in this flow passage, in which the ultrasonic transducer comprises a piezoelectric material having electrodes on the opposed surfaces thereof, one of which is used as a transmitting/receiving surface, with this transmitting/receiving surface facing the flow passage, and at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface of the piezoelectric material is divided into plural sections, and all of electrodes disposed on the divided section are electrically connected through conductors.
An ultrasonic flowmeter according to a first aspect of the invention includes a flow passage, and an ultrasonic transducer disposed for measuring the flow rate of the fluid in this flow passage, in which the ultrasonic transducer comprises a piezoelectric material having electrodes on the opposed surfaces thereof, one of which is used as a transmitting/receiving surface, with this transmitting/receiving surface facing the flow passage, and at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface of the piezoelectric material is divided into plural sections, and all of electrodes disposed on the divided section are electrically connected through conductors, and the piezoelectric material, by dividing at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface into plural sections, is capable of separating the longitudinal vibration and undesired vibration mode, and therefore the ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained, so that the ultrasonic flowmeter of high accuracy and compact size is realized.
An ultrasonic flowmeter according to a second aspect of the invention includes a parallel flow passage having a gap of a specified height at a specified position and having a specified width, and an ultrasonic transducer disposed for measuring the flow rate of the fluid in this flow passage, in which the ultrasonic transducer comprises a piezoelectric material having electrodes on the opposed surfaces thereof, one of which is used as a transmitting/receiving surface, with this transmitting/receiving surface facing the flow passage, and at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface of the piezoelectric material is divided into plural sections, and all of electrodes disposed on the divided section are electrically connected through conductors, and the piezoelectric material, by dividing at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface into plural sections, is capable of separating the longitudinal vibration and undesired vibration mode, and therefore the ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained, and moreover by forming the cross section of the flow passage into a rectangular form, the flow velocity distribution in the section of the flow passage can be simplified, and the flow rate can be deduced at high accuracy from the obtained flow velocity, so that the ultrasonic flowmeter of high accuracy is realized.
An ultrasonic flowmeter according to a third aspect of the invention includes a flow passage, and an ultrasonic transducer disposed for measuring the flow rate of the fluid in this flow passage, in which the ultrasonic transducer comprises plural piezoelectric materials having electrodes on the opposed surfaces thereof, one of which is used as a transmitting/receiving surface, with this transmitting/receiving surface facing the flow passage, and at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface of the piezoelectric material is divided into plural sections, and all of electrodes disposed on the divided section are individually connected with conductors, and the conductors are sufficiently thin as compared with the wavelength of the ultrasonic wave generated from the ultrasonic transducer, and hence the piezoelectric material, by dividing at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface into plural sections, is capable of separating the thickness longitudinal vibration and undesired vibration mode, while the electrodes can be connected without having effects on the characteristic of the ultrasonic transducer and handling of the piezoelectric material is easy, and therefore the ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained, so that the ultrasonic flowmeter of high accuracy is realized.
An ultrasonic flowmeter according to a fourth aspect of the invention includes a parallel flow passage having a gap of a specified height at a specified position and having a specified width, and an ultrasonic transducer disposed for measuring the flow rate of the fluid in this flow passage, in which the ultrasonic transducer comprises a piezoelectric material having electrodes on the opposed surfaces thereof, one of which is used as a transmitting/receiving surface, with this transmitting/receiving surface facing the flow passage, and the piezoelectric material divides at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface into plural sections, and all of electrodes disposed on the divided section are electrically connected through conductors, and the conductors are sufficiently thin as compared with the wavelength of the ultrasonic wave generated from the ultrasonic transducer, and hence the piezoelectric material, by dividing at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface into plural sections, is capable of separating the longitudinal vibration and undesired vibration mode, while the electrodes can be connected without having effects on the characteristic of the ultrasonic transducer and handling of the piezoelectric material is easy, and therefore the ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained, and moreover by forming the cross section of the flow passage into a rectangular form, the flow velocity distribution in the section of the flow passage can be simplified, and the flow rate can be deduced at high accuracy from the obtained flow velocity, so that the ultrasonic flowmeter of high accuracy is realized.
In the ultrasonic flowmeter of the fourth aspect, when the conductors are composed in a cylindrical case with a top incorporating the piezoelectric material and having the ceiling electrically connected with all of electrodes disposed on the divided section of the piezoelectric material, in an electric charge is accumulated in the piezoelectric y material to spark, since the piezoelectric material is incorporated in the cylindrical case with a top having the ceiling, the safety can be assured if the fluid to be measured is flammable gas or flammable liquid, and an accurate and compact ultrasonic flowmeter of high safety is obtained.
An ultrasonic flowmeter according to a fifth aspect of the invention relates to the ultrasonic flowmeter of the first to fourth aspects, in which at least one of the transmitting/receiving surface of the piezoelectric material and the surface confronting this transmitting/receiving surface is divided into plural sections by forming a groove, and the thickness longitudinal vibration and undesired vibration mode can be separated by this groove, and therefore the ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained, so that the ultrasonic flowmeter of high accuracy and compact size is realized.
In the ultrasonic flowmeter of the fifth aspect, the groove divides the piezoelectric material in such a depth that the vibration in the electrode direction vertical to the transmitting/receiving surface may be the main mode, and the depth of the groove is 90% or more and less than 100% of the thickness in the direction vertical to the transmitting/receiving surface, and therefore the piezoelectric material is not separated completely, and it is easy to handle the piezoelectric material, and moreover the thickness longitudinal vibration and the undesired vibration mode can be separated to degrees free from practical problem, and therefore the ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained, so that the ultrasonic flowmeter of high accuracy and compact size is realized.
Also in the ultrasonic flowmeter of the fifth aspect, the lengths of the longitudinal and lateral sides divided by the groove are set so that the vibration in the direction vertical to the transmitting/receiving surface may be the main mode, and the ratio of the lengths of the longitudinal and lateral sides divided by the groove to the thickness is all 0.8 or less, and therefore the longitudinal vibration and the undesired vibration mode can be separated to degrees free from practical problem and the thickness longitudinal vibration can be used as the main mode, and therefore the ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained, so that the ultrasonic flowmeter of high accuracy and compact size is realized.
Further in the ultrasonic flowmeter of the fifth aspect, plural grooves are provided in the piezoelectric material, and therefore the ultrasonic transducer of small size, being much wider in the selection range of frequency and dimensions, is obtained, so that the ultrasonic flowmeter of high accuracy and compact size is realized.
An ultrasonic flowmeter according to a sixth aspect of the invention includes a flow passage, and an ultrasonic transducer disposed for measuring the flow rate of the fluid in this flow passage, in which the ultrasonic transducer comprises plural piezoelectric materials having electrodes on the opposed surfaces thereof, one of which is used as a transmitting/receiving surface, with this transmitting/receiving surface facing the flow passage, and each piezoelectric material is disposed so that at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface is divided into plural sections, and all of electrodes disposed on the transmitting/receiving surface of each piezoelectric material and the surface confronting this transmitting/receiving surface are electrically connected through conductors, and since plural divided piezoelectric materials are provided, effects of undesired vibration mode are small, and therefore the ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained, so that the ultrasonic flowmeter of high accuracy and compact size is realized.
In the ultrasonic flowmeter of the sixth aspect, the flow passage is a parallel flow passage having a gap of a specified height at a specified position and having a specified width, and since the sectional shape of the flow passage is formed into a rectangular form, the flow velocity distribution in the section of the flow passage can be simplified, and the flow rate can be deduced at high accuracy from the obtained flow velocity, so that the ultrasonic flowmeter of high accuracy is realized.
Also in the ultrasonic flowmeter of the sixth aspect, the conductors are sufficiently thin as compared with the wavelength of the ultrasonic wave generated from the ultrasonic transducer, and hence the electrodes can be connected without having effects on the characteristic of the ultrasonic transducer and handling of the piezoelectric material is easy, and therefore the ultrasonic transducer of high sensitivity and small size is obtained, so that the ultrasonic flowmeter of high accuracy is realized.
Further in the ultrasonic flowmeter of the sixth aspect, the all lengths of the longitudinal and lateral sides of the transmitting/receiving surface of each piezoelectric material are set so that the vibration in the electrode direction vertical to the transmitting/receiving surface may be the main mode, and the ratio of the lengths of the longitudinal and lateral sides of the transmitting/receiving surface of each piezoelectric material to the thickness is all 0.8 or less, and therefore the longitudinal vibration can be used as the main mode, and therefore the ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained, so that the ultrasonic flowmeter of high accuracy and compact size is realized.
An ultrasonic flowmeter according to a seventh aspect of the invention relates to the ultrasonic flowmeter of the first to sixth aspects, in which an acoustic matching layer is disposed on the transmitting/receiving surface of the ultrasonic transducer, and transmitting/receiving of ultrasonic waves with the fluid is easier, and the ultrasonic transducer of high accuracy is obtained, so that the ultrasonic flowmeter of higher accuracy is realized.
An ultrasonic flowmeter according to an eighth aspect of the invention relates to the ultrasonic flowmeter of the first to seventh aspects, in which a backing layer is disposed on the surface confronting the transmitting/receiving surface of the ultrasonic transducer, and the ultrasonic transducer capable of transmitting and receiving ultrasonic pulses of short ringing time can be obtained, so that the ultrasonic flowmeter of higher accuracy is realized.
An ultrasonic transducer according to a first aspect of the invention includes a piezoelectric material having electrodes on the opposed surfaces thereof, one of which is used as a transmitting/receiving surface, in which each piezoelectric material is divided by a groove at least in one of the transmitting/receiving surface and the surface confronting the transmitting/receiving surface so that the ratio of the lengths of longitudinal and lateral sides of the transmitting/receiving surface of each piezoelectric material to the thickness is all 0.6 or less, all of electrodes disposed on the divided section are electrically connected with conductors, and the thickness longitudinal vibration and undesired vibration mode can be separated to degrees free from practical problems, and the thickness longitudinal vibration can be used as the main mode, so that an ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained.
An ultrasonic transducer according to a second aspect of the invention includes a piezoelectric material having electrodes on the opposed surfaces thereof, one of which is used as a transmitting/receiving surface, in which the piezoelectric material divides at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface by a groove, the depth of the groove is 90% or more and less than 100% of the thickness enclosed by the surfaces on which the electrodes are disposed, and all of electrodes on the surfaces divided by the groove are connected electrically with conductors, and since the piezoelectric material is not separated completely, handling of the piezoelectric material is easy, and therefore the thickness longitudinal vibration and the undesired vibration mode can be separated by the groove, so that an ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained.
In the ultrasonic transducer of the second aspect, when the ratio of the lengths of longitudinal and lateral sides of the transmitting/receiving surface of the divided piezoelectric material to the thickness is all 0.6 or less, the thickness longitudinal vibration and the undesired vibration mode can be separated to such an extent free from practical problem and the thickness longitudinal vibration can be used as the main mode, so that an ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained.
An ultrasonic transducer according to a third aspect of the invention includes a plurality of piezoelectric materials having electrodes on the opposed surfaces thereof, one of which is used as a transmitting/receiving surface, in which each piezoelectric material is disposed so that at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface is divided into plural sections, the ratio of the lengths of longitudinal and lateral sides of the transmitting/receiving surface of each piezoelectric material to the thickness is all 0.6 or less, and the electrodes on the transmitting/receiving surface and on the confronting surface are individually connected with conductors, and since plural separated piezoelectric materials are used, the longitudinal vibration can be used as the main mode without significant effect of the undesired vibration mode, so that an ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained.
An ultrasonic transducer according to a fourth aspect of the invention relates to the ultrasonic transducer of the first and second aspects, in which the conductors are sufficiently thinner conductors as compared with the wavelength of the ultrasonic wave from the ultrasonic transducer, and the electrodes can be connected without having effects on the characteristics of the ultrasonic transducer, and handling of piezoelectric material is easier, so that an ultrasonic transducer of high accuracy and small size is obtained.
In the ultrasonic transducer of the fourth aspect, when the conductors are composed in a cylindrical case with a top incorporating the piezoelectric material and having the ceiling electrically connected with all of electrodes disposed on the divided section of the piezoelectric material, in an electric charge is accumulated in the piezoelectric material to ignite a spark, since the piezoelectric material is incorporated in the cylindrical case with a top having the ceiling, the safety can be assured if the propagation medium contacting with the ultrasonic transducer is flammable gas or flammable liquid, and an accurate and small ultrasonic transducer of high safety is obtained.
An ultrasonic transducer according to a fifth aspect of the invention relates to the ultrasonic transducer of the first and second aspects, in which plural grooves are provided in the piezoelectric material, so that the ultrasonic transducer of wider selection range of frequency and dimensions and small size is obtained.
An ultrasonic transducer according to a sixth aspect of the invention relates to the ultrasonic transducer of the first to fifth aspects, in which an acoustic matching layer is disposed on the transmitting/receiving surface of the ultrasonic transducer, and exchange of ultrasonic waves with the fluid to be measured is easier, so that an ultrasonic transducer of high accuracy is obtained.
An ultrasonic transducer according to a seventh aspect of the invention relates to the ultrasonic transducer of the first to sixth aspects, in which a backing layer is disposed on the surface confronting the transmitting/receiving surface of the ultrasonic transducer, so that an ultrasonic transducer capable of transmitting and receiving ultrasonic pulses of short ringing time is obtained.